This invention relates generally to airborne phased array radar and more particularly to a system for controlling array transmitter-receiver microwave module temperature in the radar.
A phased array radar is made of many transmitter-receiver microwave modules, each having at least one antenna. When these antennas are grouped together, they form a planar antenna array. The radar beam is electronically scanned by varying the signal phase from module to module. The RF, IF and DC signals are supplied to and received from the modules by electrical distribution manifolds on the end of the module opposite the antenna.
In addition to the antenna, each module is made up of thin film microwave integrated transmitter and receiver circuitry consisting of solid-state power amplifiers, frequency multipliers, low noise amplifiers and phasors. Present state-of-the-art yields microwave devices with inherently low efficiencies, hence each device within the circuit dissipates power in the form of heat.
Various system considerations constrain the design of the radar array thermal control system. For example, low device junction temperatures are required for reliability. In addition, state-of-the-art circuit design requires a constant temperature be maintained for proper circuit operation, since many module properties, including phase, change with temperature. It is easily recognized that if each module assumed a different temperature, and thus different phase, relative to the surrounding modules that it would be impossible to predict system performance, since performance is phase dependent.
Perhaps the most critical problem in the design and operation of a phased array, is the removal of a vast amount of heat from a small volume. This of course results from the inherent nature of the device in having a large number of inefficient modules confined to a relatively small volume. In removing this heat, it is necessary to maintain a low electronic device temperature to obtain a high system reliability. Also a low temperature gradient must be maintained within the module and from module to module, since the module electrical parameters are temperature dependent. Further, the average value of the array temperature must be controlled since the modules function properly over a small temperature band, thus necessitating on occasion, the need to add heat prior to initially energizing the system to insure that it has reached operating temperature.